Functions and Structure of Ribosomes: Small Organelles that Carry Out the Process of Translation

Ribosomes are small organelles made of RNA and protein that carry out the important work of translating mRNA templates into proteins.

Ribosome Structure – Subunits of RNA and Protein

Ribosomes in eukaryotes are made up of two subunits, a large subunit, called 60-S, and a small subunit, named 40-S. In prokaryotes, the subunits are 50-S and 30-S.

These two subunits are made in the nucleus and join together in the cytoplasm to create the ribosome whenever mRNA is present and proteins need to be made. The two subunits join together, hook onto the mRNA and start protein synthesis. During the production of proteins, the larger subunit binds to tRNA and amino acids and the small subunit binds to the mRNA template. When the ribosome finishes reading the mRNA and making the protein, the two subunits break apart again.

Function of Ribosomes – Protein Construction

The function of ribosomes is to make proteins in a process called protein synthesis. The ribosomes combine amino acids, the building blocks of proteins, in the order specified by a messenger RNA (mRNA) template.

As the ribosome moves along the mRNA and reads the sequence, amino acids are attached to and organized by transfer RNA (tRNA), a special type of RNA that can bind to both the ribosome and amino acids.

Location of Ribosomes in the Cell – Free and Attached Ribosomes

Ribosomes come in two types, free ribosomes and membrane bound ribosomes, which can be found in different places within the cell and carry out slightly different versions of protein synthesis.

Free ribosomes are found floating in the cytosol of the cell, the liquid that fills the cell interior. Free ribosomes can move around in the cytosol and they generally make proteins for use inside the cell.

Membrane bound ribosomes, also called attached ribosomes, attach to the endoplasmic reticulum, creating rough endoplasmic reticulum, RER. These rough ER ribosomes make proteins that will be exported for use outside the cell or used in cell membranes. The proteins generated by ribosomes in the rough ER travel into the ER and are then packaged for transport to the plasma membrane to be incorporated there or sent outside the cell.

Ribosomes are capable of chaning between one type and another. Free ribosomes can become membrane-bound ribosomes and vice-versa depending on what the cell needs at any given time.

It is important for students of biology to understand the function and structure of ribosomes, since these important organelles carry out the steps of protein synthesis that create all of the proteins in the body. Without ribosomes, there would be no protein construction and no work could ever get done inside or out of the cell.

Small Sand Dwellers and Filter Feeders: Eight Unusual Animal Phyla Recognised by Specialists

Large filter feeders (some whales, bivalve molluscs, and barnacles for example) are well known, but the smaller ones are often obscure. Life between grains of sand or mud implies tiny size, which means that these animals are also unfamiliar – rarely seen without the aid of a microscope.

Rotifers, Micrognathozoa, and Gnathostomulids

  • The 100 or so species in the phylum Gnathostomulida are small marine animals. Most are less than 1 mm long, and they scrape food off sand or mud grains, especially in places where there is little oxygen. Gnathostomulid mouthparts suggest that they are related to the rotifers.
  • Micrognathozoa have their own phylum – even though only one species is known so far. Limnognathia maerski was discovered in Greenland in 1994, living in spring water. The animal is minute, less than one tenth of a millimeter long, and therefore one of the smallest known. Very little is known about this phylum, but it is thought to be close to the Rotifera.
  • Rotifers (Phylum Rotifera) are common in fresh water. There are over 2,000 described species of rotifer, and they were discovered early in the dawn of microscopy (by John Harris in 1696). They are able to survive long periods dehydrated, rather like the tardigrades, and this explains how they can get from pond to pond – as bits of ‘dust’ blown in on the wind. Most are less than a millimeter long, and they feed by filtering small particles (fish waste, dead bacteria, algae etc.) at the prodigious rate of 100,000 times their own volume per hour. They are ecologically important for this reason – helping to keep fresh water clean.

(Look at a ‘Gallery of Rotifer Images’).

Gastrotrichs and Kinorhynchs

  • Gastrotrichs are very small and short-lived (most only living for a few days). They typically live between sand grains as part of the ‘meiofauna’. There are about 700 species in this phylum, and it is not at all clear which other phyla are closest to them – body form suggests one set of possibilities, genetic studies another.
  • The 150 or so kinorhynchs, or ‘Mud Dragons’, also live in mud and sand, where they eat diatoms. Like the gastrotrichs it is unclear how this phylum fits in, in the evolutionary sense.

Brachiopods, Bryozoans, and Xenoturbellids

  • Brachiopods are often large animals with two shell valves, much like bivalve molluscs, but they are not closely related to them (or any of the Phylum Mollusca). 99% of all brachiopods are extinct, and those that remain are sessile filter feeders. They usually attach to the substrate by means of a long stalk.
  • Bryozoans (or ectoprocts), with over 8,000 living species, usually built tough calcareous casings for their colonies. This group of small individuals is often called a ‘sea mat’, and it is permanently attached to a rock or large plant. The individuals filter seawater. It is thought that the bryozoans are most closely related to the brachiopods.
  • The phylum Xenoturbellida consists of two known species. They are worm-like and were once thought to be related to the molluscs (because molecular studies indicated the presence of molluscan DNA), but it is now thought that this DNA gets into the animals because they either eat, or parasitise, molluscs. They have a very simple body plan, and very little is known about them.

The animals in seven of these phyla are too small for most people to notice, and the brachiopods (the eighth phylum) will normally be encountered as fossils. As fossils the brachiopods can easily be mistaken for bivalve molluscs.

Getting Electricity from Sewage

Treating human waste is a very expensive problem for most countries. Without treatment, raw sewage can spread disease and kill off the living organisms in our streams and rivers. Contamination of drinking water with sewage is common in countries that do not have the resources to treat their sewage. Sewage treatment is expensive but it does protect our waterways and prevents a lot of human illness. Unfortunately, the need to treat human sewage will never go away as long as people continue to gather together in the cities and towns of our world. About 60 percent of the human waste generated in the U.S. goes to waste treatment plants. Fourteen billion gallons of water are needed each day to carry that waste to the treatment plants. Even so about 10 percent of the waste mentioned above is not treated and goes in the form of raw sewage into our streams and rivers.

There are sewage treatment plants all over the industrialized world that utilize two relatively simple means to treat the sewage. The primary means used to treat sewage is to allow the solid material to settle to the bottom of a sedimentation tank. The sludge that settles to the bottom is pumped into an oxygen-free digester (anaerobic; secondary treatment). There, anaerobic bacteria help to breakdown many of the organic (carbon-containing) compounds in the sludge. The sludge is then allowed to dry and can oftentimes be used a fertilizer.

The liquid on top of the sludge in the sedimentation tank is then pumped to an oxygen (aerobic) containing digester (secondary treatment). The bacteria in the digester then breakdown the organic (carbon-containing) material in the sewage. The biological oxygen demand (BOD) is determined when assessing whether a digester has done its job or not. BOD is the amount of oxygen needed to breakdown the organic material in the sewage. If the sewage were released without this treatment the organisms in the waterways would use up valuable oxygen to breakdown the organic materials killing the fish and other animals dependant on oxygen in the water. By the time treated water is released around 90 percent of the BOD is removed. The water is chlorinated to eliminate most of the bacteria and then the water is released.

All of this takes time and large amounts of electricity to pump the liquids and to aerate (put oxygen in) the sewage. Some researchers from Pennsylvania State University (PSU) have found a very simple way to generate electricity from this sewage and at the same time reduce the BOD by 80 percent. In the Environmental Science and Technology (volume 38, number 7, pages 2281-2285), Hong

We Know the Enemy and It is US!

Whooping cough also called pertussis is a rare disease due to a bacterium called Bordetella pertussis. The classic signs of this disease are usually seen in children and include cold-like symptoms, a runny nose, scratchy eyes, and low-grade fever, followed by severe coughing spells that can last 1-2 minutes. These coughing spells can occur for 1-6 weeks with an average of 15 coughing spells per day with the spells being more common at night. These long episodes of coughing end in a whoop-like sound.. During the coughing spell the child may turn blue. Vomiting and exhaustion usually follow these coughing spells.

Severe complications can occur and include pneumonia, seizures, encephalopathy (damage to the brain), and death. The most common complication being pneumonia. The younger the person is when getting the disease the more likely they are to have complications. For instance 70 percent of children under 6 months of age with pertussis need to be hospitalized however, less than 10 percent of 5-9 year olds need to be hospitalized.

Fortunately pertussis is a rare disease. It is rare because a vaccine is now given to nearly all children in the industrialized world to prevent this disease. The vaccine was given to children starting in the 1940’s. In the last few years a newer and safer vaccine is routinely given to children. As a result, only about 3,700 pertussis cases per year have been reported in the United States since 1980. However, before routine vaccination programs were begun for this disease over 200,000 cases per year of pertussis were reported in the United States alone. In countries that can’t afford or do not require routine pertussis vaccination whooping cough is still a major health problem for their children. This preventable disease still kills over 300,000 children each year in the world.

Unfortunately, pertussis vaccination cannot be stopped even if all childhood pertussis were prevented. Pertussis vaccination is given when children are young. The last pertussis shot is administered when the child is 4-6 years of age. With time immunity to this bacterium goes down and teenagers and adults can get pertussis. The symptoms in teenagers and adults are less severe. Usually the person has a chronic cough (lasts longer than 7 days). Coughing episodes can end with gagging or vomiting however complications are rare. In some studies up to 13 percent of adults with chronic cough have pertussis. These teenagers and adults with pertussis can infect children that have not been vaccinated.

Physical and Behavioral Attributes of Bonobos: Differences Between Pygmy Chimpanzees and Other Great Apes

Bonobos, or pygmy chimpanzees (Pan paniscus), live in the tropical forest region of Congo. Since their discovery, debate has ensued over whether or not pygmy chimpanzees are a distinct species or a subspecies of the common chimpanzee. Whatever the case, bonobos do possess a substantial number of physical and behavioral characteristics that are distinct from those of common chimpanzees.

Physical Differences

Bonobos and chimpanzees differ in their skull size and shape, with the bonobos’ being smaller. Bonobos have a lower body weight and also differ from chimpanzees in sexual variation / dimorphism (bonobos being less dimorphic), and blood type.

Behavioral Differences

Behaviorally, bonobos differentiate from common chimpanzees in terms of social groups and patterns, food and nutrition, sexual behavior, and social relationships.

Social Groups

In general, the social groups of pygmy chimpanzees are larger than those of common chimpanzees. As well, pygmy groups are more stable and aggregative than those of common chimpanzees; conflicts are resolved more peacefully and the individual survival rate is higher.

Food and Nutrition

In terms of food, common chimpanzees seem to eat a larger quantity and variety of food types. It is unclear, however, whether or not this is a result of the diversity and amount of food available in the two species’ respective habitats. Common chimpanzees, for example, “exploit a wider ecological range to obtain food than pygmy chimpanzees and have developed a higher degree of technical skills. Conversely, the food acquisition skills of pygmy chimpanzees are primarily for obtaining fruits in high trees” (Kano 1992, p. 137).

Sexual Behavior

Bonobos are also unique in their patterns of sexual behavior. Females are nearly always sexually receptive, have friendships with males and other females, and are sexually promiscuous. As a result, there is little sexual competition among males, particularly compared to common chimpanzees.

Social Relationships

Social relationships are more coherent among bonobos. Unity among males is less strong than in common chimpanzees; however, relationships among females and between male and female bonobos are much friendlier than in common chimpanzees (Kano 1992, p. 205). In general then, pygmy chimpanzees have large, stable groups made up of nearly equal numbers of males and females. In contrast to common chimpanzees, bonobos are passive, do not engage in all-male war parties, and have never been witnessed to carry out infanticide (Kano 1992, p. 209; Rumbaugh 1998, p. 3).

Given the stark differences between chimpanzees and bonobos, researchers have been anxious to examine whether or not bonobos would demonstrate a higher (or lower) capacity for human language learning. Because of their temperament and inquisitive nature, it has been proposed that they may be better adept at language training tasks and it has been suggested that bonobos are more intelligent than common chimpanzees.

Anatomy of a Sea Kayak: Basic Components of Interest to Paddlers

Native kayaks like the one shown in the picture from Nunivak above were the forerunners of the modern sea kayaks we use today. While they share similar shapes and purposes, little else is similar in their construction, stability, or safety. Generally, sea kayaks are longer and more tapered at the ends compared to their river cousins. A touring sea kayak will be around sixteen feet (4.9 meters) long and have a beam of about 25 inches (63.5 centimeters). Most kayak safety experts recommend using a sea kayak that is at least thirteen feet (4 meters) long.

Construction – Native kayaks used a framework to support the skin used to form the hulls of their craft. Except for folding kayaks, modern sea kayaks use materials that require no internal framework to function. Building materials come in two classes, composites and plastics:

  • Composites – These are laminated material like fiberglass, carbon fiber and Kevlar bonded together with polyester or epoxy resin. Composite kayaks are expensive and subject to abrasion on barnacle encrusted, rocky beaches. They are however much lighter in weight.
  • Plastics – Plastic kayaks are roto-molded, that is, formed in slowly spinning molds that shape them. Common plastic materials used in kayaks are linear polyethylene and cross-linked polyethylene. Cross-linked polyethylene is the tougher of the two choices and hold up well in rough beach conditions. Plastic kayaks will weigh more than ten pounds (4.5 kilograms) than a similarly shaped composite craft.

Positive Flotation – Modern sea kayaks are designed with watertight flotation compartments and unused voids in the hull are often filled with foam. Chambers installed forward and aft of the cockpit have watertight hatches and are used to store gear. A touring kayak can easily carry camping equipment and food for a week or more.

Kayak Cockpit – The paddler sits low in the kayak cockpit. Sea kayaks are designed so that the paddler is near the bottom of the hull, which keeps the center of gravity low and improves the stability of the craft. The cockpit has a combing or lip around it to facilitate use of a spray skirt/paddle jacket to keep out water. Many cockpits will have thigh braces that help stabilize the paddler within the kayak. Rudder pedals are located inside the cockpit. There is usually room in the cockpit for a water bottle, a small dry sack and emergency gear like a marine VHF radio.

Deck Fittings – Sea kayaks have a number of important features associated with their decks.

  • Lifting Toggles – These are handles usually formed of plastic that are attached to each end of the kayak with a short piece of cord.
  • Deck Bungies – There are bungies installed forward and aft of the cockpit that allow readily accessible gear to be carried on the deck. This can be a spare paddle, a bilge pump or a chart.
  • Compass – Many sea kayaks have a magnetic compass mounted into the combing forward of the cockpit. Learning to use a chart and compass is an important seamanship skill. They make excellent backups for a GPS receiver with a dead battery.
  • Watertight Hatch Covers – Watertight compartments will have hatch covers in place to prevent entry of water. Many hatch designs use a neoprene cover that fits under the hatch itself. Hatch covers are usually held in place with nylon straps and buckles.
  • Rudder Tripping Line – Kayaks equipped with a rudder will have a line running up near the cockpit that allows the paddler to raise and lower the rudder. It is a good practice to raise the rudder before beaching a kayak.
  • Life Line – Some sea kayaks will have a line running around the outside edge of the deck that provides a grab point for a person in the water reaching for the kayak.